The present invention relates to a structure of the rotor of a superconductive rotary electric machine.
An example of a conventional rotor of a superconductive rotary electric machine is shown in FIG. 1. The figure illustrates one end of a coil-carrying shaft 2 for the stator and the end portions of the superconductive magnetic field coils 3. Reference numeral 2 denotes the coil-carrying shaft; 16 the coil end keeper sleeve; 21 an electrically insulating layer; 22 an insulating cover; and 23 electrically insulating fillers.
FIG. 2 is a perspective view showing the end of the coil-carrying shaft 2 for an easy understanding of FIG. 1. Like numerals represent like parts.
In FIGS. 1 and 2 the superconductive field coils 3 are accommodated in the recessed portion of the coil-carrying shaft 2 and the spaces between the coils 3 and recessed portion are filled by the fillers 23. The keeper sleeve 16 is tightly fitted around the coil-carrying shaft 2 by a shrinkage fit method to press against the entire periphery of the shaft 2 so that the field coils 3 are very firmly kept in the correct positions.
The conventional electrically insulating fillers 23 which extend in an axial and circumferential directions of the coil-carrying shaft 2 are tightly engaged with the shaft 2 as shown in FIGS. 1 and 2. Accordingly the following problems are encountered when the electrically insulating fillers 23 are inserted into gaps between the superconductive magnetic field coils 3 and into gaps between the superconductive field coils 3 and the coil-carrying shaft 2.
One superconductive magnetic field coil 3 comprises a plurality of turns. The turns are electrically from each other. The electric insulation is accomplished by means of electrically insulating tapes wound on the coil conductors in a spiral manner. The insulating tapes are subject to insulation-breakdown when the insulating fillers 23 are inserted. The insulation breakdown of the tapes between turns of coil may cause short circuiting of the coils, resulting in the stopping of the operation of the rotary machine. When the gaps between the insulating fillers 23 and the superconductive field coils 3 at the outer periphery are smaller than those at the inner periphery, gaps are formed between the under side face of the superconductive field coils 3 and the insulating fillers 23, resulting in loose fitting of the under portion of the superconductive field coil 3. In such circumstance, the superconductive field coils are displaced due to the electromagnetic and centrifugal forces during the operation so that frictional heat is generated, which may hinder the operation of the rotary electric machine.
FIG. 3 shows an alternative conventional arrangement in which insulating fillers are divided into a plurality of padding plates which are mounted to cover the sides of the superconductive field coils and the filler portions. The insulating padding plates 23a cover the entire side faces of the superconductive field coils 3 and the filler portions 23b are provided in the other positions. After the superconductive field coils 3 have been mounted on the coil-carrying shaft 2, the sides of the superconductive field coils 3 are covered by the insulating padding plates 23a, then the insulating fillers 23b are inserted. The superconductive field coils 3 are firmly secured without breaking the insulation between respective turns of the superconductive field coils 3 by the aforementioned method of the assembly.
However the aforementioned arrangement still has the following disadvantages. It is impossible to secure the superconductive field coils 3 so that the sides of the field coils 3 are not flush with each other no matter how carefully carried out in the securing of the superconductive field coils 3 to the coil-carrying shaft 2. Accordingly all the turns of the superconductive field coils 3 are firmly pressed by the padding plates 23a.